I wasn't expecting these questions.
For barb,How do you polarize a spin?
The Stern-Gerlach experiment
was an early demonstration of electron spin. In the diagram, two beams of particles emerge from the apparatus, one containing electrons with spin polarized "up" and one with electrons having spin polarized "down". The axis of the spin is set by the magnetic field lines across the input particle beam.How do you send it?
AFAIK, the particles carrying the spin are going fast through a vacuum. (It seems Alice is also entangling multiple electrons with their spins oriented antiparallel, i.e. opposite)How does Bob read it?
Not that I understand this, but Bob uses "quantum metrology" which is the advance reported by the researchers. It uses "quantum walks" to obtain a more accurate direction in space than could be had by conventional methods. This depends on the spins being entangled.